Field of the Invention
The present invention relates to a method of application, and more particularly to a method in which a magnetic liquid, a surface protective liquid, an undercoat liquid, a lubricating liquid or the like is applied to a long wide flexible carrier such as a plastic film, paper, foil or the like so that a thin liquid film is disposed on the carrier for manufacturing an application-type magnetic recording medium. Additionally the invention relates to an apparatus for doing the same.
Each application-type magnetic recording medium mentioned herein is manufactured by applying a liquid having a desired thickness to the surface of a nonmagnetic flexible band-like carrier (which is hereinafter referred to as a web) being continuously conveyed in a prescribed path and is thereafter dried. Therefore, the application-type magnetic recording medium is very different in regard to the manufacturing process from a magnetic recording medium of so-called non-application type, which is manufactured through ion plating, sputtering, vacuum evaporative deposition or the like.
Most magnetic recording media manufactured and sold for audio, video and data processing machines are still of the application type. Although some of the media of the application type are manufactured using a gravure application method, a reverse roller application method, a doctor blade application method and so forth, most of the media are manufactured in an extrusion-type application method because the products manufactured in this manner are higher in stability and lower in cost than those manufactured in the former methods. However, the extrusion-type application method has disadvantages in that the web is scraped using an extrusion-type application head resulting in the web becoming streaked or contaminated. This problem is more likely to arise at the beginning or end of the application of the liquid to the web, particularly when the slot of the outlet edge portion of the extrusion-type application head is protrusively disposed at a prescribed lap angle to the web supported on the path rollers. Accordingly, the scraping of the web by the head and the resulting streak on the film of the applied liquid are much more likely to occur at the initial stage of the application of the liquid to the web.
To solve these problems, an extrusion-type application method was proposed as disclosed in Japan Patent Application (OPI) No. 95169/87 (the term "OPI" as used herein means an "unexamined published application"). In the method, the applying head of the device and a web are moved relative to each other and the timing of the contact of the head with the web and the subsequent discharge of liquid are controlled.
However, the above-mentioned problems cannot completely be solved by the application device and the application method disclosed in the above-mentioned Japanese Patent Application. In other words, chips are likely to be scraped from the web by the edge of the head at the beginning of the application and become trapped at the upstream edge of the doctor edge portion of the application head of the device resulting in streaking of the liquid film on the web.
In recent years, it has become more apparent that the speed of the web when applying liquid thereto has been increased to enhance the quality and recording density of an application-type magnetic recording medium and improved the productivity therefor. Along with that trend, problems relating to the streaks on the web and the scraping of the web at the beginning of the application have become more severe. Specifically, the streaks and the scraping of the web tend to occur more often as the application speed is increased. This is also a problem.
The present invention was made in consideration of the above problems. Accordingly, it is an object of the invention to provide a method of applying a liquid so as to very precisely prevent the occurrence of a streak and/or a longitudinal streak, to consistently manufacture a high-quality magnetic recording medium with high yield and productivity.